As an interactive device having simple producing process and with low producing cost, the infra-red touch screen develops fast in recent years and be vastly applied in various fields. The basic structure of an infra-red touch screen includes multiple pairs of infra-red emitting elements and infra-red receiving elements arranged at edges around a display surface suit for installment according to a special sequence. The above infra-red emitting elements and infra-red receiving elements are made emitting-receiving pairs according to one to one correspondence. The emitting-receiving pairs are perpendicularly arranged at the edge of the display surface to form an emitting-receiving array, under control of micro computer system, each emitting-receiving pair is connected by infra-red rays. By detecting whether the infra-red rays between the infra-red emitting element and the infra-red receiving element of each pair are blocked, whether a touch event occurs is determined.
In the conventional infra-red touch screen system, the rays form a grid on the display surface, while detecting touch, the coordinates of the position where the touch event occurs may be calculated by determining the position of the nodes of the grid where the touch occurs. The way of the conventional detecting makes the detecting system receive only one group of coordinate data in a predetermined time, so if there is only one touch point, the touch screen will work fine, however, if there are more than two touch points, the system will result in wrong coordinates.
Mechanically, the conventional system generally has optical signal emitting devices 1 and optical signal receiving devices 2, wherein each of the optical signal emitting devices 1 is uniquely corresponds to an optical signal receiving device 2. According to the above principal, by placing a plurality of the optical signal emitting devices 1 and the optical signal receiving device 2 around a display screen and by making the rays emitted by the optical signal emitting devices 1 be uniformly distributed in the display area of the display screen, if a user uses fingers or other stuff like pens to touch some position on the display screen, the fingers or the other stuff will block the optical signals emitted by the optical signal emitting devices 1 and the corresponding optical signal receiving devices 2 will not receive the optical signals, further, by using data processing platform to calculate the position the fingers or stuff locate to achieve determining the position the fingers or the other stuff locate on the display screen. However, if more than two touch points display on the display screen, locating the touch points by the above technology will generate high rate of misreading. For example, as shown in FIG. 1 and FIG. 2, if there is a touch point A in FIG. 1, the position will be accurately determined by the above technology, however if there are two points in FIG. 2, the two points may be identified to be A1,A1 or A2,A2 by the above technology, such that misreading occurs.
Besides the above technology, there are some infra-red touch screens utilizing a third direction scanning which can eliminate two ghost points when two points touching happens, however, when the touch points are increased, the method also fail to work, moreover, the method cannot determine the size of the touch points.
Based on the above reasons, the conventional infra-red touch screen technology may fail to work in a circumstance need multiple touches like multiple players game, multiple fingers drawing and so on, which limit the infra-red touch screen to be used in more fields.